Liquid crystal display

Abstract

An LCD displays an image having gradations according to a dithering technique. The LCD is capable of canceling a direct-current voltage applied to a liquid crystal panel of the LCD. The LCD has an A-D converter for achieving a dithering operation according to reference voltage pairs that are switched from one to another. The LCD employs a phase control signal 20 to control the phase of the dithering operation. The logic value of the phase control signal 20 is changed to switch the reference voltage pairs with respect to a given one of the polarities of a LCD driving voltage applied to the panel. When data provided by the A-D converter involve different gradations, a voltage difference is generated between the LCD driving voltages of different polarities. This voltage difference produces a direct-current voltage in the panel. The present invention cancels the generated direct-current voltage, to prevent images from being stuck into the panel.

We claim: 
     
       1. A liquid crystal display, comprising, an analog-to-digital converter;   a liquid crystal panel having signal and scanning electrodes;   means for switching at least two reference voltages from one to another at first intervals for input to the analog-to-digital converter to quantize an analog image signal into display data according to a dithering technique;   means for using the display data to prepare signals applied to the signal electrodes of the panel;   means for applying a select signal to the scanning electrodes, the signals applied to the signal and scanning electrodes of the panel having alternate polarities to display on the panel an image with gradations,;   said at least two reference voltages being divided into two groups, each of said two groups being alternately synchronized with one of the polarities of the select signal applied to one of the scanning electrodes at second intervals, each of said second intervals being two times longer than each of the first intervals at which the at least two reference voltages are switched from one to another.   
     
     
       2. A liquid crystal display, comprising; an analog-to-digital converter;   a liquid crystal panel having signal and scanning electrodes;   means for switching at least two reference voltages from one to another at first intervals for input to the analog-to-digital converter to quantize an analog image signal into display data according to a dithering technique;   means for using the display data to prepare signals applied to the signal electrodes of the panel;   means for applying a select signal to the scanning electrodes, the signals applied to the signal and scanning electrodes of the panel having alternate polarities to display on the panel an image with gradations,;   said at least two reference voltages being divided into two groups, each of said two groups being alternately synchronized with one of the polarities of the select signal applied to one of the scanning electrodes at random intervals, each of said random intervals being two times longer than each of the first intervals at which the at least two reference voltages are switched from one to another.   
     
     
       3. The liquid crystal display of claim 1 wherein the at least two reference voltages comprise two reference voltage pairs. 
     
     
       4. The liquid crystal display of claim 2 wherein the at least two reference voltages comprise two reference voltage pairs.